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  <title>Raise an arbitrary precision number to another, reduced by a specified modulus</title>
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  <div id="layout-content"><div id="function.bcpowmod" class="refentry">
 <div class="refnamediv">
  <h1 class="refname">bcpowmod</h1>
  <p class="verinfo">(PHP 5, PHP 7)</p><p class="refpurpose"><span class="refname">bcpowmod</span> &mdash; <span class="dc-title">Raise an arbitrary precision number to another, reduced by a specified modulus</span></p>

 </div>
 
 <div class="refsect1 description" id="refsect1-function.bcpowmod-description">
  <h3 class="title">说明</h3>
  <div class="methodsynopsis dc-description">
   <span class="methodname"><strong>bcpowmod</strong></span>
    ( <span class="methodparam"><span class="type">string</span> <code class="parameter">$base</code></span>
   , <span class="methodparam"><span class="type">string</span> <code class="parameter">$exponent</code></span>
   , <span class="methodparam"><span class="type">string</span> <code class="parameter">$modulus</code></span>
   [, <span class="methodparam"><span class="type">int</span> <code class="parameter">$scale</code><span class="initializer"> = 0</span></span>
  ] ) : <span class="type">string</span></div>

  <p class="para rdfs-comment">
   Use the fast-exponentiation method to raise 
   <code class="parameter">base</code> to the power
   <code class="parameter">exponent</code> with respect to the modulus
   <code class="parameter">modulus</code>.
  </p>
 </div>


 <div class="refsect1 parameters" id="refsect1-function.bcpowmod-parameters">
  <h3 class="title">参数</h3>
  <p class="para">
   <dl>

    
     <dt>
<code class="parameter">base</code></dt>

     <dd>

      <p class="para">
       The base, as an integral string (i.e. the scale has to be zero).
      </p>
     </dd>

    
    
     <dt>
<code class="parameter">exponent</code></dt>

     <dd>

      <p class="para">
       The exponent, as an non-negative, integral string (i.e. the scale has to be zero).
      </p>
     </dd>

    
    
     <dt>
<code class="parameter">modulus</code></dt>

     <dd>

      <p class="para">
       The modulus, as an integral string (i.e. the scale has to be zero).
      </p>
     </dd>

    
    <dt>
<code class="parameter">
scale</code></dt>
<dd>
<p class="para">此可选参数用于设置结果中小数点后的小数位数。也可通过使用
<span class="function"><a href="bcscale.html" class="function">bcscale()</a></span> 来设置全局默认的小数位数，用于所有函数。
</p></dd>

   </dl>

  </p>
 </div>


 <div class="refsect1 returnvalues" id="refsect1-function.bcpowmod-returnvalues">
  <h3 class="title">返回值</h3>
  <p class="para">
   Returns the result as a string, or <strong><code>NULL</code></strong> if <code class="parameter">modulus</code>
   is <em>0</em> or <code class="parameter">exponent</code> is negative.
  </p>
 </div>

 
 <div class="refsect1 notes" id="refsect1-function.bcpowmod-notes">
  <h3 class="title">注释</h3>
  <blockquote class="note"><p><strong class="note">Note</strong>: 
   <p class="para">
    Because this method uses the modulus operation, numbers which are not
    positive integers may give unexpected results.
   </p>
  </p></blockquote>
 </div>

 
 <div class="refsect1 examples" id="refsect1-function.bcpowmod-examples">
  <h3 class="title">范例</h3>
  <p class="para">
   The following two statements are functionally identical.  The
   <span class="function"><strong>bcpowmod()</strong></span> version however, executes in
   less time and can accept larger parameters.
   <div class="informalexample">
    <div class="example-contents">
<div class="phpcode"><pre><span style="color: #000000">
<span style="color: #0000BB">&lt;?php<br />$a&nbsp;</span><span style="color: #007700">=&nbsp;</span><span style="color: #0000BB">bcpowmod</span><span style="color: #007700">(</span><span style="color: #0000BB">$x</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">$y</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">$mod</span><span style="color: #007700">);<br /><br /></span><span style="color: #0000BB">$b&nbsp;</span><span style="color: #007700">=&nbsp;</span><span style="color: #0000BB">bcmod</span><span style="color: #007700">(</span><span style="color: #0000BB">bcpow</span><span style="color: #007700">(</span><span style="color: #0000BB">$x</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">$y</span><span style="color: #007700">),&nbsp;</span><span style="color: #0000BB">$mod</span><span style="color: #007700">);<br /><br /></span><span style="color: #FF8000">//&nbsp;$a&nbsp;and&nbsp;$b&nbsp;are&nbsp;equal&nbsp;to&nbsp;each&nbsp;other.<br /><br /></span><span style="color: #0000BB">?&gt;</span>
</span>
</pre></div>
    </div>

   </div>
  </p>
 </div>

 
 <div class="refsect1 seealso" id="refsect1-function.bcpowmod-seealso">
  <h3 class="title">参见</h3>
  <p class="para">
   <ul class="simplelist">
    <li class="member"><span class="function"><a href="bcpow.html" class="function" rel="rdfs-seeAlso">bcpow()</a> - 任意精度数字的乘方</span></li>
    <li class="member"><span class="function"><a href="bcmod.html" class="function" rel="rdfs-seeAlso">bcmod()</a> - 对一个任意精度数字取模</span></li>
   </ul>
  </p>
 </div>

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